This patent application claims a benefit of priority from Italian Patent Application No. MI99A001608 filed Jul. 21, 1999, through PCT Application Serial No. PCT/IT00/00301 filed Jul. 19, 2000, the contents of each of which are incorporated herein by reference.
The present invention relates to an electrosurgical probe for tumor treatment by radiofrequency energy, and particularly to a probe containing a plurality of needle-shaped electrodes whose tips can be expanded at the tumor to be treated so as to affect a volume of cancer tissue which is as large as possible.
The tumor treatment by hyperthermia which is induced by radiofrequency energy or other energy forms is already known in medicine. Electrosurgical probes provided with needle-shaped electrodes which, by penetrating into the cancer tissue, cause its necrosis, have already been developed.
International Publication No. WO 96/29146 describes electrosurgical probes comprising independent needle-shaped electrodes which are pushed inside the tissue to be treated by making them come out from the point of a metal cannula inserted into the patient""s body. This is obtained by using electrodes formed of thin metal wires having an arched end provided with elastic memory which is kept in a substantially stretched condition inside the cannula and is released, expanding itself, when the electrodes are pushed out of the cannula in order to penetrate into the tissue to be treated. An object of this expansion is that a volume of cancer tissue to be treated which is as large as possible is affected.
U.S. Pat. No. 5,813,855 and International Publication No. WO 98/52480 describe other electrosurgical probes which are also formed of a rigid cannula containing one or a plurality of filiform electrodes having arched tips with elastic memory which are compressed inside the cannula in a stretched position and which expand themselves when they are pushed out of the cannula inserted inside the tissue to be treated. The filiform electrodes are arranged inside the cannula around a central nucleon so that, when their tips are pushed out from the point of the cannula, the cancer tissue is affected in a regular volume which is as similar as possible to a sphere.
However, none of the presently known electrosurgical probes is capable of creating an electrical field having a real spherical shape, but rather, in the known electrosurgical probes, it is at the most possible to obtain an electrical field having an ellipsoidal shape since, as is apparent from FIGS. 4 and 5 of WO 98/52480, only a small portion of the distal end of the metal cannula which participates to the formation of the electrical field is surrounded by the arched ends of the filiform electrodes.
Another drawback of the known electrosurgical probes is that their use involves the risk that the arched ends of the electrodes, by penetrating into the cancer tissue under the impulse of the suitable control, may go beyond the appointed target and penetrate also in vital structures, for instance a blood vessel, adjacent to the portion to be treated.
Therefore, an object of the present invention is to provide an electrosurgical probe of the type with multiple needles having an arched point with elastic memory which is free from the above mentioned drawbacks.
This object is achieved by the electrosurgical probe having a cannula having a plurality of holes and a distal end and a proximal end and a plurality of filiform electrodes housed in the cannula and having an elastic memory of an arched shape. The number of electrodes corresponds to the number of holes in the cannula and each hole has a size to allow passage of a respective electrode therethrough. A control rod is movably arranged in the cannula and has a distal end and a proximal end. The electrodes are fixed to the distal end of the control rod and have a free end extending toward the proximal end of the cannula when housed therein. Each electrode is arranged to move rearward in the cannula to pass through a respective hole in the cannula and then to arch forward toward the distal end of the cannula upon pulling the proximal end of the control rod in a rearward direction. As such, the movement of the electrodes in the cannula and the direction of pulling of the control rod are in the same rearward direction.
The electrosurgical probe according to the present invention eliminates the first of the above mentioned drawbacks of the probes according to the prior art, because it has the important feature that the electrodes, when they are outside the cannula, are arranged like the meridians of an ideal sphere whose diameter is formed of a long segment of the cannula distal portion, which is not coated by the insulating material. Accordingly, also the cannula in its distal portion participates in creating the active field of the radiofrequency. As a matter of fact, when the needle-shaped electrodes protrude from the cannula, the arched portion of each electrode forms an arc of 180xc2x0 whose two ends are located near to the two ends of the uncoated distal portion of the cannula, that is, near to the two poles of the ideal sphere of which that portion of the cannula forms the diameter.
The second of the above mentioned drawbacks of the known electrosurgical probes is eliminated by means of the probe according to the present invention because it has the feature that the expansion of the arched tips of the electrodes is controlled by traction of the electrodes and not by thrust like in the known probes. In other words, whereas in the known probes the expansion of the filiform electrodes is controlled by a movement in the same direction of penetration of the electrodes into the patient""s tissues, in the probe according to the present invention, the expansion is controlled by traction, that is by a movement in the opposite direction with respect to that of penetration of the electrodes into the patient""s tissues. As a result, the free end of each filiform electrode will have the tendency to converge, after the expansion movement, towards the distal end of the metal cannula, thus avoiding the risk that it may diverge towards vital structures and perforate them. This is due to the fact that in the probe according to the present invention, in the rest position thereof, both the filiform electrodes and the rod which controls them have the same direction but they are turned in different directions after the expansion.
Besides eliminating the above mentioned drawbacks of the probes according to the prior art, the electrosurgical probe according to the present invention offers another important advantage, that is preventing, during this operation, the electrodes from coming out accidentally from the probe point during the positioning operation of the probe itself into the tissue. This is due to the fact that the operation for causing the electrodes expansion takes place by retraction with a movement in the opposite direction with respect to the positioning movement, and not in the same direction like in the prior art.
A further advantage of the electrosurgical probe according to the present invention with respect to the prior art is that no free space between the distal end of the cannula and the content thereof is provided. As a matter of fact, this free space, which is present in the known probes, may cause undesired phenomena of core boring of healthy tissue of the patient during the probe positioning operation. The structure of the probe according to the present invention allows also to close the distal end of the cannula and to confer it a pointed tip.